A recording material making use of color development based on a chemical reaction between a color forming dye and a developer is capable of carrying out a recording process in a relatively simple apparatus and within a short period of time without performing complicated processing such as development fixing. Thus, such recording material is used in a wide range of applications including pressuresensitive copying materials or thermal recording materials of output-recording units employed in facsimile machines or printers.
The capability to develop colors quickly and maintain the whiteness of the portion with no developed colors is demanded of these recording materials. The portion with no developed colors is hereafter referred to as the background. In addition, high durability of background and image is demanded of these recording materials. In recent years, particularly, a large amount of recording material is being used in a field where the reliability of a recorded image is considered to be of high importance. As a result, there is an increase in the demand for a recording material having an excellent image stability such as heat and humidity, heat, light, water and plasticizer (included in a macromolecular material) resistance.
With one kind of developer, however, it is difficult to provide a recording material satisfying all the demands described above. In addition, while attempts have been made to use a mixture consisting of a developer exhibiting a good heat and humidity resistance and a developer having a good light resistance, a recording material that sufficiently satisfies all the requirements has not yet been invented. As described earlier, the requirements include an excellent sensitivity in recording, heat and humidity, heat, light, plasticizer and water resistance. When a recording material does not satisfy all the requirements, a phenomenon called background fogging typically occurs after the creation of a piece of thermal recording paper. A background fogging is a phenomenon in which color is generated on the thermal recording paper.